XPTI Vulnerability in Xen Hypervisor Affecting Guest Page Table Isolation

CVE-2026-79609

What is CVE-2026-79609?

The vulnerability involves a flaw in the Xen Hypervisor's implementation of Xen Page Table Isolation (XPTI), which was designed to mitigate Meltdown vulnerabilities. The issue arises from the handling of 64-bit paravirtualized (PV) guest page table entries copied from guest-specified root page tables to those chosen by Xen. Given that the PV guest’s directmap does not encompass all memory due to segmentation beyond the 5 TiB address boundary, this creates potential lapses in protection, enabling unauthorized access to memory regions that should be isolated.

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